It has been known for a long time to have a radiation source using groups of light sources which emit light having different wavelengths, see for example from U.S. Pat. No. 4,568,558 and also EP 879 582. In the case of the first-mentioned solution, dental material is intended firstly to be partly polymerized with a wavelength of between 400 and 450 nm and subsequently to be completely polymerized with a wavelength of 350 nm. By contrast, LED chips having various wavelengths such as 435, 450 and 470 nm are intended to be used in the case of the second-mentioned solution.
The LEDs are arranged in bundled fashion and are uniformly supplied with voltage, with the result that selective driving is not possible. Different photoinitiators having different spectral sensitivities cannot be taken into account with this solution.
In the last 10 years numerous investigations have been undertaken in order to improve the effectiveness of the photopolymerization, in order to enable shorter treatment cycles for the dentist or, if appropriate, the dental technician without jeopardizing the reliability of the dental restoration upon full curing.
Accordingly, various photopolymerizable materials have been investigated and used, there generally having been the tendency to realize a greatest possible spectral overlap between the emission spectra of the light sources used and the sensitivity spectra of the photoiniators used. This of course necessitates the use of different spectral emission spectra which have been striven for in different photoinitiators.
Recently, so-called dual-curing systems have also been proposed, the solution
in accordance with U.S. Pat. No. 6,866,506 enabling the curing result to be significantly improved. This solution provides two semiconductor radiation sources having different emission maxima which are spaced apart from one another and are each, in particular, at different points in time.
In the case of this solution, however, a multiplicity of chips is used for providing the light power, so that this solution is more likely to be considered for high-quality light curing devices. In order to provide the desired curing, use is made of chips having high light emission which are comparatively expensive, moreover, and which emit an intensive light radiation. This is all the more so since, in the case of this solution, the curing is performed by a respective group of chips successively, so that a subgroup of the chips must also have a power sufficient for the curing.